Research on numerical abilities in deaf children (DC) is scarce and results contradictory. The education type, the presence of cochlear implants, short-term memory (STM) skills or the language level, have been put forward as explanatory factors for differences in mathematics between DC and hearing children (HC). To investigate the influence of language and STM on numerical abilities in 9-year-old DC with cochlear implants and HC, following regular education, while controlling for age, sex and non-verbal cognitive level. The results show lower performance in DC in STM and language. Regarding numerical abilities, DC showed lower performance than HC on arithmetic tasks, a difference that remained significant after controlling for STM but not for language. While STM does not appear to explain differences between DC and HC, language level appears to contribute to exact number skills. These data must be taken into account in the care and education of deaf children.